Method of and means for operating a tuned radio receiver



1929. A. s. BLATTERMAN 1,713,463

METHOD OF AND MEANS FOR OPERATING 'A TUNED RADIO RECEIVER I Original Filed May 21, 1925 Patented May 14, 1929.

UNITED STAT-ES 1,713,463 PATENT OFFICE.

ALBERT S. BLATTERIAN, OF NORTH ASBUBY PARK, NEW JERSEY, ASSIGKOB '10 3. I. C. PATENT COKTANY, OI TBENTON, NEW JERSEY, A CORPORATION NEW Your.

METHOD 0! AND MEANS FOR OPERATING A TUNED RADIO RECEIVER.

Application fled May 21, 1925, Serial No. 31,801. Renewed December 8, 1928.

trol member such as a rotatable dial. This' control would, for simple, include the simultaneous tuning of the input circuit of the receiver, of one or more stages of radio fre-- qtuency amplification and of the detector s age.

Up to the present it has been substantially impossible to secure simultaneous and equal tunin of these several circuits by means ofa sing e control element for reasons which will be lplointed out hereafter.

the drawings accompanying my specification I, show in:

Figure 1 a diagrammatic representation of a receiver havin one stage of tuned radio frequency ampli cation; and in Figure 2 a curve indicatinf between antenna capacity an wave length, which .will be referred to in my description.

It will be understood that my invention is ap licable to 'a wide variation of uses and that I o not-intend to limit myself to the particular embodiment illustrated in the draw-'- ings. Specifically, it will be understood that my invention is particularly useful where a multi-stage radio frequency amplifier is used.

Referring to Figure 1, 1 represents the antenna connected to ground at 2, variable connections to the primary 4 of the antenna tuninductance 'ng made possible through the switch 3. The antenna system is inductively coupled to the secondary 5 included in he input circuit of the first stage of radio frequency amplification; this stage including the 40 tuning condenser 6, the vacuum tube -7,-the usual B battery 8 and filament battery 9. This stage maybe coupled to another stage of amplification or to a detector. stage b means of a coupling transformer 10, 11 whic stage contains the usual tuning capacity 12 and1 the other instrumentalities ordinarily the arrangement in use at the present time, the inductan'ces 4'and 5 and 10 and 11 arefixed and the capacities 6 and ,12 jare so connected as to be operated by a common operating member 15 having a-dial 16. In such an arrangementeven if the inductances and the relation mum,

tuning condensers in the several stages are made to have identical values at all settin the s stem will not operate satisfactorily f o r the ollowing reasons. It will be seen that the capacity of the antenna circuit is reflected into the first stage of radio frequency amplifipation and that the capacity of the tube 7 is reflected into the next succeedin detector or amplifier stage. The capacity 0 the antenna circuit is a capacity of an entirely different order from the capacity of the tubes, and for this reason the transformer-condenser circuit associated with the antenna will tune in an entirely different manner from the transformer-condenser circuit associated with an amplifier stage, thus merely simultaneously varying the capacities and will not produce the desired result because the difierence in the reflected capacitieswill be felt in the several stages and will cause mistuning as a conseuence.- I

If C re 1 resents the capacity in the primary circuit 0 a transformer of the type under discussion, L, represents the inductance in the primary circuit of such a transformer and C represents the tuning capacity across the secon ary winding of such a transformer, it can be shown that the effect of the presence of the primary circuit when tightl coupled to the secondary circuit is to intr uce into the secondary circuit fromthe primary circuit an effective capacity approximately equal to The effective capacity thus introduced into the secondary circuit I have termed reflected capacity. In this type of circuit it is well known that the secondary current is manthat is, the best tuning effect is obtained when the reactance of the secondary bears to the reactance of the primary the same ratio that the square of the mutual reactance between the two'circuits bears to the square of the primary impedance. This relationship is expressed ,in formula 36, page 163, of Electric Oscillations and Electric Waves by Pierce, ublished by McGraw-Hill & Company. If i, represents the reactance of the primary circuit, X the-reactance of the secondary circuit, M the mutual inductance between the primary and secondary clrcuits,

and Z the impedance of the primary circuit,

16 ill,

For tight coupling between the primary and practical use of circuits of this type, M is approximately equal to'L,L Therefore, (3)

becomes L L i 1 w 1 2 1 25 (4) -aam na-i In practice the resonant frequency of the primary circuit is considerably below the frequencies that are being used in reception, hence o L C may be neglected in comparison with unity and. (4) becomes (5)v 119L 0 1 =wL C L C When the secondary elements L, and C are properly tuned, the quantity L,(l would exactly equal unity were it not for the presence of the primary circuit. As a close approximation we may, therefore, consider m L G =L Hence (5) becomes From Equation (7) it is at once apparent that the effective secondary capacity is greater than the actual capacity C, by the amount the fact that the secondary circuit is not isolated but is cou led to the primary circuit, which, because of this coupling, reflects to the secondary circuit a capacity equal to the value calculated, namely the secondary circuit as is customary in the This additional capacity appears because of sociated with the antenna circuit, the value of C, is the capacity of the antenna against the ground which ordinarily may be of the order of several hundred micro-micro-farads. The the case of the subsequent transformers in the amplifier stages, the value of C is the effective capacity of the vacuum tubes con nected to the primary windings of the transformers and this has a Value of the order of 10 micro-micro-farads. It is evident, there fore, that if the secondary tuning capacities C in the several stages are identical and the primary inductances L -are identical, that the antenna stage will not tune in the same way as the amplifier stages on account of the fact that 0 in the antenna stage is many times larger than C, in the amplifier stages.

I have discovered that I can compensate for this difference in the reflected capacities by introducing into the amplifier stages a capacity 13 connected between the plate and fila: ment electrodes of the vacuum tube; that is to say, in the same relative position in respect to the primary 10 of the coupling transformer as the capacity of the antenna is with respect to the primary 4 of the antenna transformer.

If more than one stage of radio frequency amplification is used, condensers similar to condenser 13 are connected in corresponding locations in each of the stages; The capacities 13 are preferably fixed condensers and have a value substantially equal to the value of the antenna capacity, for the reason that,

at a given appropriate wave length, they re- .flect into the next succeeding stage a capacity equal to the capacity reflected by the antenna into the first stage.

The arrangement just described would permit of simultaneous tuning by adjustment of condensers 6 and 12 to the same degree and mechanically connecting them to operate together, were it not for the fact that, as is well recognized the eflective capacity of the antenna varies with the wave length. In Figure 2 I have shown a curve expressing the relation between effective antenna capacity and wave length, from which it will be seen that the efi'e'ctive antenna capacity varies very greatly at short wave lengths and is substantiall constant and has relatively lower values at long Wave lengths. A consideration of this curve will make it evident that fixed compensation, as obtained by the inclusion ofcondensers such as 13, would be ineffective if the receiver is intended to operate over a relatively wide band of wave lengths and that under such conditions fixed compensation is impractical, itbeing necessary to introduce additional compensation to take care of variations in effective antenna capacity due to variations in wave length. a I have found that this additional compensation may be introduced by varying the primary inductance of the antenna circuit so as to change the capacthe inductance of the antenna circuit.

. the capacity or in circuit into the the first amity reflected from the antenna tuned secondary circuit; that is, plifier stage. As stated above, the reflected capacity in the first amplifier stage is expressed by the quantity shown on the coil 4 or by otherwise varying will also be seen that the value of this expression might be changed by varying the effective capacity of the antenna circuit (that is, the factor C by introducing additional capacity in series with the antenna; such additional capacity being illustrated by the dotted condenser 14. V

The particular mechanical means by which the condensers 6 and 12 and the switch 3 (or the condenser 14) may be simultaneously operated is shown conventionally lines 15 and 16. v

In the operation described it will be understood that the com ensating capacity 13 is chosen of such a va ue as to compensate for the smallest reflected tenna which might be experienced in the normal operation of the device, that is to say, the reflected capacity appropriate to the longest wave length the receiver is adapted to receive. For shorter wave lengths the reflected capacity is decreased by decreasing the inductance or capacity of the antenna circuit, as stated above. That is to say decreasing the factors L, or C, or both. When decreasing the product L C, of the antenna circuit for shorter wave lengths,'either by decreasing 'ductance of the antenna cir-. cuit, there results a looser coupling of the antennawith the first amplifier stage, a desirable result in an apparatus of this character and which produces an increase in signal strength, it being generally recognized that looser couplings for shorter wave lengths and tighter couplings for longer wavelengths give a more uniform transfer of the received signals throughout the wave length band to which the receiver may be tuned.

While I have described my invention in one of its preferred forms, there are many possible changes and variations and these I desire to include within the scope of my claims.

I claim: 7

1. In a vacuum tube radio receiver including at least one stage of tuned frequency amplification and a tuned detector. stage, the

combination with tuning means in each stage by the dotted capacity 'due to the ani mechanically connected together for simultaneous operation, of means for providing a fixed com ensation in each stage after the first for t e capacity reflected from the antenna circuit into the input circuit of the first stage at a given wave length, and means in the antenna circuit adapted to be adjusted by operation of said tuning means for maintaining said reflected capacity substantially constant regardless of variations of wave length from said given wave length.

2. In a vacuum tube radio receiver including at least one stage of tuned radio frequency amplification and a tuned detector stage, the

combination with coupling transformers between the antenna and the first stage and be- 1; tween the successive stages, and tuning means in each stage mechanically connected together for simultaneous operation, of means for providing a fixed compensation in each stage after the first for the capacity reflected from the antenna circuit into the input circuit of the first stage at'a given wave length, andmeans in the antenna circuit operable by mani ulation of said tuning means for maintaining said reflected capacity substantially constant regardless of variations of wave length from said given wave 1e 3. In a vacuum tube radio receiver including at least one stage of tuned radio frequency amplification and a tuned detector stage, the combination with coupling transformers between the antenna and the first stage and between=the successive stages,'and tuning means associated with the secondary of each transformer mechanically connected together for simultaneous. operation, 0 means associated with the primary of each transformer after the first for providing a fixed compensation for the capacity reflected from the antenna circuit into the secondary of the first transformer at a given wave length, and means in the antenna circuit operable by manipulation of said tuning means for maintaining said reflected capacity substantially constant regardless of variations connected together for simultaneous operation, of fixed condensers connected across the primary of each transformer after the first, the capacity of each fixed condenser being substantially equal to the effective capacity of the antenna circuit length the set is adapted to receive, and means operable by manipulation of said tuning condensers for maintaining the effective capacity introduced into the secondary of the at the longest waves transformer by the antenna circuit coupled thereto substantially constant.

5. The method of operating vacuum tube radio receivers comprising at least one sta e of tunedradio frequency amplification an a tuned detector stage, each stage having similar tuning elements adapted to be operated simultaneously by a common control, which comprises compensatingin each sta e after 10 the first for the capacity reflected into the first stage from the antenna circuit at a given ALBERT S. BLATTERMAN. 

